Process for manufacturing acid phosphate or superphosphate



W. T. DOYLE.

PROCESS FOR MANUFACTURING ACID PHOSPHATE 0R SUPERPHOSPHATE.

APPLICATION FILED .IANJO, I92I.

Patented July 5, ML

2 SHEETS-SHEET l W. T. DOYLE.

PROCESS FOR MANUFACTURING ACID PHOSPHATE 0R SUPERPHOSPHATE.

APPLICATION FILED JAN.10, I921.

mam]; 2m Patented Ju1y5,l921.

2 SHEETS-SHEET 2- Al arny law rs vore;-

: WELIAM T. DOYLI'L OF BOSTON, MASSACHUSETTS, ASSIGNOIR TO STURTEVANTMILL COMPANY, OF BOSTON, MASSACHUSETTS, A CORPORATION OF MASSACHUSETTS.

PROCESS FOR MANUFACTURING ACID PHOSPHATE OR SUPERPHOSPHATE.

Specification of Letters Patent.

mam July 5, rear.

Application filed. January 10, 1921. Serial No. 436,021.

To all whom it may concern:

Be it known that I, WILLIAM T. DOYLE,

provement in Processes for Manufacturing Acid Phosphate orSuperphosphate, of which the following description, in connection withthe accompanying drawings, is a specification, likecharacters on thedrawings representing like parts.

This invention relates to a process for preparing acid phosphate orsuperphosphate.

One important source of acid phosphate is in a phosphate rock which isfound in Florida, Tennessee and other places. This rock containsphosphoric acid as tribasic phosphate of lime which is insoluble inwater, and consequently when applied to the soil, cannot be assimilatedby plants. Therefore, it is necessary to convert the insolublephosphoric acid in phosphate rock into soluble phosphoric acid. 1 Thisis accomplished usually by treating the ground rock phosphate withsulfuric acid or hydrochloric acid which removes two parts of the limeas gypsum and leaves one part of the lime combined with phosphoric acidas monobasic or acid phosphate of lime soluble in water.

Heretofore, the ground phosphate rock and dilute sulfuric acid, forexample, 1,000 lbs. of each, are introduced into a mixer where themasses are thoroughly mixed and then discharged into a large chambergenerally built-of concrete and known as a den.

A chemical reaction takes place in this den which generates heat, whichin turn converts the water of the dilute sulfuric acid into steam. Y

The mixture is allowedto stand about twelve hours in the den, and thenit is broken down or disintegrated, removed and conveyed to a curingpile, where it is allowed to remain a sufficient length of time for thechemical reaction to continue, and further convert insoluble phosphoricacid into soluble phosphoric acid.

There are certain objections to the method heretofore practised. Noxiousfumes accompanying the chemical reaction taking place in the den arevery objectionable and injurious to workmen employed in removing thematerial from the den and in conveying the same to the curing pile. Oneof the purposes of the present invention, therefore, is to draw thesteam and noxious fumes from the den, so that the workmen may remove thematerial from the den witho t injury to them from the poisonous gases.

The acid phosphates coming from the den have a certain percentage offree phosphoric acid which renders them damp and sticky, so that theytend to pack down and solidify. The acid phosphates cannot be sold tothe farmer in this condition, because they would clog and not passthrough a planter or other machine for applying the phosphates to thesoil. Another purpose of the invention, therefore, is to remove themoisture from the materials, so as to render the same in dry andpulverulent condition for ready application to the soil. In carry-' ingthis feature of the invention into practical effect, the materialsconveyed from the den are broken up and a current of air is has not hadtime to combine with the phosphate of lime so as to be converted intophosphoric acid, and also there is a certain amount of free phosphoricacid in the mixture. Another purpose of the invention, therefore, is tointroduce finely ground or pulverized phosphate rock to the materialtaken from the den to combine with the free sulfuric acid and phosphoricacid, and convert the phosphate of lime into phosphoric acid, therebymaterially increasing the amount of phosphoric acid obtained from thecharge of materials introduced into the den. The cost of the addedfinely ground phosphate rock is very much less than the cost of the acidphosphate, so that by the addition of this finely ground phosphate rockto the mixture, an important economy is obtairo led in the production ofthe phosphoric ac1 By the present invention, the drying process and theaddition of the finely ground phosphate rock to the mixture coming fromthe den may be continuously carried on, and the insoluble phosphoricacid may be converted into soluble phosphoric acid without the necessityfor allowing the materials to stand a long period in a curing ile toobrials may be so treated that they will be in .readiness for shipmentwithin a short period, such, for example, as about a week, to allow thesame to cool. This reduces the size of the plant required for themanufacture of the acid phosphate, and it elimihates the necessity forstorage of a large stock of the acid phosphate to meet the shippingrequirements.

With the aforesaid and other purposes in view, the character of theinvention will be best understood by reference to the followingdescription of the process which may be practised in the apparatus shownin the accompanying drawings, wherein Figure l is a verticallongitudinal section through one form of apparatus embodying theinvention;

Fig. 2 is .a vertical transverse section through the apparatus;

Fig. 3 on an enlarged scale is a vertical section taken on line 3-3 ofFig. 1;

Fig. i is a horizontal section taken on line 4-4 of Fig. 2; and

Figs. 5 and 6 on an enlarged scale are details'of the conveyer.

Referring to the drawings, the apparatus shown therein may besubstantially the sameas that disclosed in my copending applies-.15 tionSerial No. 365,558, filed March 13, 1920.

This apparatus comprises a mixer 1 of usual construction, into which theground phosphate rock and the sulfuric acid may be mixed.

' A suitable den 2 may be provided to re ceive the materials from themixer. In the present instance, this den comprises vertical walls 3 anda roof 5 conveniently of concrete, one of the walls having a door 7 toadmit the workmen into the den. At the bott m of the den is a floor 9which may have an elongated opening 11 (Fig.. 3) therein, which may becovered by a series of boards 13.

Beneath the den is a housing 14 containing an endless conveyer, in thepresent instance, comprising a pair of sprocketwheels 15 on a shaft 17,and sprocket wheels 19 on a shaft 21. These sprocket wheels may beconnected by sprocket chains 23 which may carry trough sections 25 ofsuflicient length so as to overlap in the upper horizontal run thereof,and in effect provide a continuous trough for receiving materialsdeliveredfrom the den through the elongated opening 1, as more fullyhereinafter described. The upper horizontal runs of the sprocket chai'nsmay. be guided by bars 27 supported on frames 29. 1

After the mixture has remained in the den four hours, the workmen mayenter the den through the door 7 and progressively lift the boards 13 onthe floor above the elon gated slot 11, and by means of picks or othersuitable means break down or disintegrate the materials and deliver thesame through the slot 11 onto the endless conveyer.

As stated, steam and noxious fumes are generated in the den, and thematerials leave the same in a moist condition. Next will be describedthe means for drawing the steam and noxious fumes from the den, and fordrying the surfaces of the materials as they are conducted from the denby the conveyer. This means, in the present instance, comprises a pipeor conduit 29 havingone end communicating with the housing 14 referredto, adjacent the delivery end of the conve yer. A blower or fan 31 ofwell known construction may be provided in a box 33 communicating with,the pipe 29, said fan being driven by a pulley 35 from any suitablesource of power.

The construction is such that on rotation of the fan a suction efi'ectwillbe' roduced in the pipe 29 and the housing 14 w ich will draw thesteam and noxious fumes from the den, and produce an air draft: abovethe materials carried by the conveyer so as to tend to remove moisturefrom saidma'terials.

The materials delivered from the conveyer are in lump-or closely compactform,

and therefore, it 'is desirable to break up or disintegrate the sameinto finely divided or pulverulent form. To accomplish this, a hopper 37may be provided having its upper end communicating with the housing 14adjacent the delivery end of 'the' con-' veyer, so that the materialsmaybe delivered by the conveyer into said hopper. At thelower end of thehopper 37 is a device for breaking up the materials, conveniently 'inthe form of a-slicer, in the present instance, comprising bluntarms orbars 39 projecting from a hub 41 fast on a vertical shaft 43 journaledin bearings 45 and 47. At the meshing with a bevel gear 51 fast on ahorizontal shaft 53 journaled in bearings 55 and hogper.

uitable means may be provided for adding the pulverulent phosphate rockto the materials delivered from the conveyer into the hopper 37. It isdesirable that a predetermined amount of this pulverulent rock shallbeadded to the materials. For exupper end of said shaft is a bevel gear49 ample, if the charge of ground phosphate rock and sulfuric acidintroduced into the den is 2,000 lbs., the proportion of pulverulentphosphate rock added may desirably be 50 lbs, but this proportion may bevaried more or less.

The pulverulent phosphate rock to be added may be introduced into achamber 61 having a delivery hopper 63 at the lower end thereof,provided with a discharge mouth 65 and a gate or valve 67 for controllinthe discharge from said mouth.

weighing apparatus may be provided beneath the hopper 63, in the presentinstance, comprising a weighing receptacle 71 carried adjacent one endof a weighing beam 73 fulcrumed on a support 75 intermediate the ends ofsaid beam. A weight 77 may be provided on the beam to counterbalance theweight of the receptacle 71, and the beam may be provided w1th a poise79 which may be adjusted along the beam to different positions accordingto the weight of pulverulent phosphate rock to be introducedinto theweighing receptacle.

Suitable means may be provided to conduct the materials from the weighinreceptacle into the delivery end of the casing 14 above the hopper 37.This means, in the present instance, comprises a tube 81 containing ascrew conveyer 83 which may be rotated by suitable means. instance, thismeans comprises a ratchet, 85 fast on the screw conveyer shaft 87, andadapted to be advanced step by step by pawls 89 on a pair of arms 91projecting from the lever 93 fulcrumed on the shaft 87 The lower end ofthis lever may be adjustably connected to onev end of a link 95, theopposite end of which may be connected to a wrist pin 97 adapted to setin any of a series of holes 99 located at different radial distancesfrom the axis of a disk 101 mounted on a horizontal shaft 103 journaledin bearings 105, said shaft having a pulley 107 thereon adapted to bedriven from any suitable source of .power.

The construction is such that a charge of the finely ground phosphaterock to be added may be fed from the weighing receptacle 71 by the screwconveyer 88 into the delivery end of the housing 14 above the hopper 37.Here it will combine with the materials delivered by the endlessconveyer from the den, and will be mixed with said materials as they aredelivered from said hopper and broken up by the rotary slicer.

Suitable means may be provided for causing a current of air to passthrough the materials delivered from the hopper 37, in ordercontinuously to remove the moisture therefrom. To accomplish this, inthe present instance,-a receiving-hopper 111 may be provided beneath thehopper 37, and a box 113 may be provided at the upper end In the presentthereof. The lower end 117 of this box may be open, and the Wall 119 ofthe box may have a diameter less than the mouth of the receiving hopper111 to afford an annular air inlet 121.

- A 'pipe or air conduit 123 may have its lower end communicating withthe box 113 through the top thereof, and the upper end of said pipe maybe connected to and con1- municate with the pipe 29 referred to.

-The construction is such that the'blower or fan 31 provided for thepipe 29 will cause a current of air to flow downward through the annularinlet 121 into the receiving hopper 111, and thence upward through thebox 113 and pipe 123. This air current will come in contact with thematerials pulverized by the slicer, and remove moisture therefrom.

The materials may be delivered from the receiving hopper 111 and beconveyed by a car or other suitable means to the place desired, so as tobe in readiness for shipment.

The operation of the apparatus will be readily understood. The finelyground phosphate rock and the sulfuric acid are introduced in equalparts by weight into the mixer, and delivered therefrom into the den.The materials are allowed to stand in the den about twenty-four hours toallow the chemical reaction to take place which converts the insolublephospporic acid into soluble phosphoric acid. owever, all of theinsoluble phosphoric acid is not converted into soluble phosphoric acidin the den. The workmen may progressively lift the boards 13 and pickdown and eliver the materials from the den through the elongated passage11 to the conveyer. The latter will conduct the materials from theden'to the hopper 37 The mixture contains a certain amount of freesulfuric acid which has not had sulficient time to combine with thephosphate of lime and be converted into phosphoric acid,

and also contains a certain amount of free phosphoric acid.

By the introduction. of the dry, finely ground phosphate of lime intothe mixture as it is delivered to the hopper, the free sulfuric acid andphosphoric acid may com-- bine with the finely ground phosphate rock andconvert the latter into phosphoric acid. Thus, the percentage ofphosphoric acid. obtained from the charge originally introduced into theden is materially increased; The value of the added ground phosphaterock is very much less than the value of the acid phosphate, andtherefore, the addition of the ground phosphate rock to utilize the freesulfuric acid and phosphoric acid of the charge efi'ects animportantsaving.

The blower will draw the steam and noxious fumes from the den throughthe conveycr housing and away therefrom so as to enable the workmen toenter the den and pick down and deliver the mixture from the den to theconveyer without discomfort or injury therefrom, and the current of airpassing over the mixture being conveyed will tend to dry the surfaceportions of themix-. ture, but a substantial amount of moisture stillremains in the mixture, which tends to cause the particles thereof toadhere together in the form of lumps and confine the moisture therein.It is, therefore, desirable to break up or pulverize the mixturedelivered from the conveyer, in order to liberate the moisturetherefrom, This is accomplished by the rotary slicer which operates athigh speed and thoroughly breaks up anti guberizes the materialsdelivered from th opper.

The moisture thus liberated is removed from the materials by the currentof air,

which flows downward through the annular inlet, and thence upwardthrough the box and pipe leading to the blower. This current of aircomes into contact with the materials broken up and whirled in the boxat the upper end of the hopper, and effectively removes the liberatedmoisture there'- from. This intensive air treatment of the materialsthus broken up dries the same sufficientl sov that the materials are incondition or shipment after they have stood for a few days to allow thematerials time to cool, since the free sulfuric acid and hosphoric acidhave combined with the finely ground phosphate rock substantially tocomplete the chemical reaction of the sulfuric acid, the insolublephosphoric acid of the mixture is converted into soluble phosphoric acidin sufiicient amount, so that it is unnecessary to transfer the mixtureto a curing pile and allow the same to stand from thirty to sixty daysas has heretofore been necessary, in order to allow the chemicalreaction to be com leted, but, on the con- .herein, and that variousdeviations may be made therefrom without departing from the spirit andscope of the appended claims.

\Vhat is. claimed is '1. A process of manufacturing acid phosphatecharacterized by mixing ground phosphate rock and sulfuric acid, storingthe mixture for a period, pulverizing the mixture, adding pulverulentphosphate rock to the mixture to take up free sulfuric acid andphosphoric ac1d therein, and removlng the steam and fumes from themixture.

2. A process for manufacturing acid phosphate characterized by mixingground phosphate rock and acid, storing the mixture for a period,breaking up the mixture to liberate moisture therefrom, and removing themoisture from the mixture.

3. A process 'for manufacturing acid phosphate characterized by mixingvground phosphate rock and dilute sulfuric acid, storing the mixture toallow conversion of insoluble phosphoric acid into soluble phosphoricacid, and solidification of the mixture, disintegrating the mixture andadding pulverulent phosphate rock to the mixture to take up freesulfuric acid and phosphoric'acid from the mixture. v

4. A process for manufacturing acid phosphate characterized by mixingground phosphate rock and acid, storing the mixture to allow chemicalreaction to convert insoluble phosphoric acid into soluble phosphoricacid, breaking up the mixture to liberate vapor therefrom, andexhausting from the mixture the vapor thus liberated therefrom.

5. A process for manufacturing acid phosphate characterized by mixingground phosphate rock and acid to form solidacid phosphate, pulve'rizingthe solid mixture and addingpulverulent phosphate rock to the mixture toincrease the phosphoric acid available therefrom.

. 6. -A process for manufacturing acid phosphate characterized by mixingground phosphate rock and acid, pulverizing the mixture and addingpulverulent phosphate rock to the mixture to increase the phosphoricacid available therefrom, and passing an air current through thepulverized mixture to remove vapor therefrom.

7. A process for manufacturing acid phosphate characterized by mixingground phosphate rock and dilute sulfuric acid to form solid acidphosphate, pulverizing the mixture, and adding pulverulent phosphaterock to the mixture to increase the available phosphoric acid therein.

In testimony whereof, I have signed my name to this specification.

wiLLiAM 'r. DOYLE.

